DCP01B SERIES
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SBVS012C − DECEMBER 2000 − REVISED AUGUST 2005
cycle so that all devices discharge together. A subsequent
charge cycle is only restarted when the last device has
finished its discharge cycle.
APPLICATION INFORMATION
The DCP01B, DCV01, and DCP02 are three families of
miniature DC/DC converters providing an isolated
unregulated voltage output. All are fabricated using a
CMOS/DMOS process with the DCP01B replacing the
familiar DCP01 family that was fabricated from a bipolar
process. The DCP02 is essentially an extension of the
DCP01B family providing a higher power output with a
significantly improved load regulation, and the DCV01 is
tested to a higher isolation voltage.
OPTIMIZING PERFORMANCE
Optimum performance can only be achieved if the device
is correctly supported. By the very nature of a switching
converter, it requires power to be instantly available when
it switches on. If the converter has DMOS switching
transistors, the fast edges will create a high current
demand on the input supply. This transient load placed on
the input is supplied by the external input decoupling
capacitor, thus maintaining the input voltage. Therefore,
the input supply does not see this transient (this is an
analogy to high-speed digital circuits). The positioning of
the capacitor is critical and must be placed as close as
possible to the input pins and connected via a
low-impedance path.
TRANSFORMER DRIVE CIRCUIT
Transformer drive transistors have a characteristically low
value of transistor on resistance (RDS); thus, more power
is transferred to the transformer. The transformer drive
circuit is limited by the base current available to switch on
the power transistors driving the transformer and the
characteristic current gain (beta), resulting in a slower
turn-on time. Consequently, more power is dissipated
within the transistor. This results in a lower overall
efficiency, particularly at higher output load currents.
The optimum performance is primarily dependent on two
factors:
1. Connection of the input and output circuits for
minimal loss.
SELF-SYNCHRONIZATION
2. The ability of the decoupling capacitors to maintain
the input and output voltages at a constant level.
The input synchronizations facility (SYNCIN), allows for
easy synchronizing of multiple devices. If two to eight
devices (maximum) have their respective SYNCIN pins
connected together, then all devices will be synchronized.
PCB Design
The copper losses (resistance and inductance) can be
minimized by the use of mutual ground and power planes
(tracks) where possible. If that is not possible, use wide
tracks to reduce the losses. If several devices are being
powered from a common power source, a star-connected
system for the track must be deployed; devices must not
be connected in series, as this will cascade the resistive
losses. The position of the decoupling capacitors is
important. They must be as close to the devices as
possible in order to reduce losses. See the PCB Layout
section for more details.
Each device has its own onboard oscillator. This is
generated by charging a capacitor from a constant current
and producing a ramp. When this ramp passes a
threshold, an internal switch is activated that discharges
the capacitor to a second threshold before the cycle is
repeated.
When several devices are connected together, all the
internal capacitors are charged simultaneously.
When one device passes its threshold during the charge
cycle, it starts the discharge cycle. All the other devices
sense this falling voltage and, likewise, initiate a discharge
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